Simulation of On-Off Control with Hysterisis

On Off controllers (also known as bang-bang controllers) are simple
examples of feedback controllers. The are commonly encountered in
thermostats, used to control temperature in many electrical devices.
This app simulates an on off controller with hysteresis used to
control a first order process with delay process. Many heating and
cooling processes can be modelled as a first order process with time
delay.

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How to use

The process parameters are keyed into the cells C6 through C8.
For the controller, only has the hysteresis parameter to be set.
This parameter represents the percentage by which the process value
has to move before the controller changes state. For instance,
hysteresis of 10% means that the process value must move over 10% of
its range over the setpoint before the controller turns off.

Obviously, controllers with high hysteresis values are not
desirable, higher hysteresis means that the process value will swing
through a larger range. The following screenshots illustrate this,
they show behaviour of controllers with different hysteresis
controlling the same process. Note that the variation in the process
value is larger when the controller has larger hysteresis.